Parturient hypocalcemia is a metabolic disease of lactating animals, such as dairy cows, and occurs as subclinical hypocalcemia around calving and in early lactation and in severe cases lactating animals contract clinical milk fever (parturient paresis). The lactation cycle of a dairy cow extends for approximately 10 month of the year immediately subsequent to calving. Lactation by dairy cows is at a minimum during the two month immediately prior to calving, and the dairy cows are normally not milked during this “dry period”. The act of calving induces lactation in the dairy cow, and milk production is at a peak by 4–6 weeks thereafter.
During the dry period, the dairy cow has a low demand for calcium, and is thus able to absorb sufficient calcium via the digestive tract by simple passive diffusion. During lactation the demand for calcium is high, which leaves the cow in a negative calcium balance, which results in the activation of the vitamin D-dependent complex mechanisms. The lactating cow is thus capable of increasing the utilisation of the feed ration calcium by increasing absorption from the digestive tract and by resorbing calcium from the skeletal system via the blood. By these active mechanisms the lactating cow is capable of covering up to 80% of its demand for calcium during lactation (Klooster, 1976). Therefore, lactating animals are capable of preventing hypocalcemia to occur due to these powerful natural defence mechanisms almost regardless of the calcium intake via the feed.
However, during the dry period these natural defence mechanisms are deactivated, as the demand for calcium is low. Upon calving and onset of lactation there is an immediate demand for high levels of calcium to be supplied via the blood circulation to the mammary glands for milk production. The calcium regulating mechanisms are not prepared for this sudden demand for calcium in the high yielding dairy cow, and it must thus contract hypocalcemia and milk fever. Symptoms of milk fever, such as lowering of body temperature, usually become manifest within one day before and four days after calving.
Extensive research has been conducted to develop methods for preventing or treating milk fever. It has been observed that the risk for milk fever is reduced when the acid-base balance of the dairy cow is manipulated by acidifying dietary ration composition (Dishington, 1982). Presently, a method based on this principle is widely used in the USA. However, acidification of dairy cows is unnatural, since urine from ruminants normally is alcaline. Furthermore, overdosage has been reported.
Another approach of preventing milk fever is the peroral drenching with calcium chloride around calving (Jørgensen, 1990). The effect of this method is interpreted as a simple calcium diffusion through the wall of the forestomach and through the wall of the small intestine. However, there are several drawbacks associated with this method. The dairy cows have to be handled and dosed individually, which involves the above mentioned problems. Furthermore, the precise calving time of the cow must be known, because the first drenching is recommended to be carried out a few hours before calving.
Injection of a synthetic D-vitamin preparation in large doses has been suggested for the prevention and/or treatment of milk fever. Although this method is documented to be effective, it is not allowed in many countries. Another suggestion involves continuous milking, which will prevent milk fever, as the calcium regulating mechanisms are constantly activated. However, this method only applicable to single cows which are known or suspected to contract milk fever, but it is not feasible at a herd level.
Ramberg et al. (1970) observed that milk fever can be controlled and/or eliminated by administering a low calcium dietary ration to dairy cows during the weeks immediately prior to calving. By feeding a low calcium dietary ration, the cow is left in a negative calcium balance, which results in the activation of its natural calcium regulating mechanisms. Unfortunately, there are many problems associated with this method. For example, most of the cattle feed, such as alfalfa and other legumes, contain too high levels of calcium to bring the dry cow in a negative calcium balance. Furthermore, the method presents a substantial problem when dealing with a large herd. To solve the above first mentioned problem, U.S. Pat. No. 3,908,020 discloses a complete, calcium-limited feed ration. However, this method implies the purchase of rather expensive feed, which is not feasible under commercial dairy farming conditions, when the farmer is using his home-grown crops for feeding.
In view of the foregoing it is evident that these currently used methods of preventing hypocalcemia involve several problems in modern farming. It is thus an important objective of the present invention to provide a novel composition and method to prevent hypocalcemia in lactating animals. The disclosed method has the advantage that its effect is based on the powerful, natural calcium regulating mechanisms of animals and at the same time it is applicable under commercial dairy farming conditions.